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When I open Unicode font in Windows Character Map it doesn't show Juktakkhor. Are they hidden in font?
No Juktakkhor is present in Unicode fonts as separate character. It is some kind of scripting system, where the font dynamically produce Juktakkhors as defined in them, like, if you type
্ (Hasanta) betwenn two
ক, the font will automatically produce
ক্ক. But if you open these fonts in Fontlab, you can see all the hidden Juktakkhors present there. Not a magic at all, this is the benifit of open type technology.
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How Unicode know which Juktakkhor to show after pressing two alphabets?
I already answered that, it is kind of scripting. These fonts know nothing magically, rather, developers write these info inside the fonts. Generally, Microsoft VOLT software (free) is used to do so.
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Which software I should use to view and create Unicode Font?
The most common combination is FontLab (version 5 or later recommended) and Microsoft VOLT. They can be downloaded from below locations:
MS VOLT
FontLab Studio (Demo Version)